In the title compound, {[Ce(C14H9N2O5)(C14H8N2O5)(H2O)2]·H2O}n, three carboxyl groups of two independent isophthalate anions are deprotonated and they bridge the CeIII cations, forming a two-dimensional polymeric structure parallel to (001); another carboxyl group is not deprotonated and links with the adjacent pyridine ring via an O—H⋯N hydrogen bond. The CeIII cation is coordinated by six O atoms from carboxyl groups and two O atoms from coordinated water mol­ecules in a distorted square-anti­prismatic arrangement. Extensive O—H⋯O and O—H⋯N hydrogen bonding occurs in the crystal structure.

The title compound, (I) was synthesized and its structure was determined by X-ray diffraction. Similar crystal structure with 5-isonicotinamidoisophthalic acid as ligand has been reported recently (Chen et al., 2011; Deng, 2011).

In the title compound, the central CeIII ion is eight-coordinated by two O atoms from two water molecules, two carboxylate O atoms from two partial-deprotonated HL- ligands and four other O atoms from four different L2- ligands, which forming a distorted square-antiprismatic geometry (Fig. 1). Moreover, the HL- anions adopt µ2-η1:η1 bridging coordination mode, while two carboxylate groups of each L2- ligand have different coordination modes, one is µ2-η1:η1 bridging and the other one acts as µ2-η2:η1-bridging coordination mode, whereas the pyridyl group is free of coordination. Such a coordination mode makes (I) into an infinite two-dimensional network (Fig. 2). The pyridyl groups are free. Adjacent molecules are linked through O—H···N and O—H···O hydrogen bonds into a three-dimensional network.

Amide H atoms were located in a difference Fourier map and refined as riding in as found relative positions, other H atoms were placed geometrically with O—H = 0.86 (water), 0.82 (carboxyl) and C—H = 0.93 Å), and refined in riding mode, Uiso(H) = 1.2Ueq(N,O,C).

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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